From a legal point of view, in many countries, although marriage is legally monogamous (a person can only have one spouse, and bigamy is illegal), adultery is not illegal, leading to a situation of de facto polygamy being allowed, although without legal recognition for non-official "spouses".
According to scientific studies, the human mating system is considered to be moderately polygynous, based on both surveys of world populations, Polygyny is the practice wherein a man has more than one wife at the same time.
He also discusses more male-dominated though relatively extensive farming systems such as those that exist in much of West Africa, in particular the West African savannah, where polygyny is desired more for the creation of sons, whose labor is valued. He notes Dorjahn's (1959) comparison of East and West Africa, showing higher female agricultural contributions in East Africa and higher polygyny rates in West Africa, especially in the West African savannah, where one finds especially high male agricultural contributions.
Goody says, "The reasons behind polygyny are sexual and reproductive rather than economic and productive" (199), arguing that men marry polygynously to maximize their fertility and to obtain large households containing many young dependent males." Polygynous marriages can be distinguished between sororal polygyny, in which the co-wives are sisters, and non-sororal, where the co-wives are not related.
Worldwide, different societies variously encourage, accept or outlaw polygamy.
Both levirate and sororate may result in a man having multiple wives.If every brother married separately and had children, family land would be split into unsustainable small plots.In Europe, this was prevented through the social practice of impartible inheritance (the disinheriting of most siblings, many of whom went on to become celibate monks and priests).Drawing on the work of Ester Boserup, Goody notes that the sexual division of labour varies between the male-dominated intensive plough-agriculture common in Eurasia and the extensive shifting horticulture found in sub-Saharan Africa.In some of the sparsely populated regions where shifting cultivation takes place in Africa, women do much of the work.